78CJ-- Use #4 if you're using copper wire from the meter to the panel, use #2 if you're using aluminum. This is for a 100 amp main. Also the ground wire from the meter base to the ground rod needs to be a minimum of #8 if copper or #6 if aluminum' (it can be insulated or bare) and be sure to buy a ground clamp and ground rod (3/4" rod 8' long).
Added: Do you have to install you meter base and weatherhead or does the electric company do this for you? If you have to do it, you'll probably need 2/0 for the tie-in to the wires coming from the transformer. If over head, be sure to leave at least 3' lead coming out of the weatherhead on all three wires for the power company to connect to.
